Welsh C F, Zhu D, Bourguignon L Y
Department of Cell Biology and Anatomy, University of Miami Medical School, Florida 33101, USA.
J Cell Physiol. 1995 Sep;164(3):605-12. doi: 10.1002/jcp.1041640319.
CD44 is a glycosylated adhesion molecule which may undergo alternative splicing of 10 possible exons to generate variant isoforms. A number of CD44 variant isoforms expressed by tumor cells have been correlated with metastatic and proliferative behavior. In this study, we have characterized CD44 isoform expression on three prostate cancer cell lines: ALVA-31, PPC-1, and LNCaP. Using reverse transcriptase-polymerase chain reaction, we have found that ALVA-31 and PPC-1 cells express multiple CD44 isoforms, including CD44s (standard form), CD44E (epithelial form), and an exon 14-containing form. In addition, two smaller forms have been detected: one using an alternative donor splice site within exon 5, and a novel form omitting exon 5 entirely. The CD44 isoforms expressed by ALVA-31 and PPC-1 cells appear to be preferentially located on the cell surface. By contrast, LNCaP cells do not express any of the CD44 forms at the RNA or protein level. Both PPC-1 and ALVA-31 cells display tumorigenesis and invasiveness in nude mice, whereas LNCap cells exhibit a less malignant phenotype, suggesting a correlation between CD44 variant (CD44v) expression and aggressive prostate tumor behavior. Functional characterization reveals that CD44 mediates prostate cell adhesion to extracellular hyaluronic acid (HA). In addition, the CD44 cytoplasmic domain binds specifically to ankyrin, a membrane cytoskeletal protein. Double immunofluorescence labeling and confocal microscopic analyses indicate that HA binding induces the HA receptor (i.e., CD44) to form capped structures. Importantly, intracellular ankyrin is preferentially accumulated underneath HA receptor-capped structures. These results suggest that cytoskeletal proteins such as ankyrin are closely associated with CD44-mediated signaling events induced by HA. Finally, HA-mediated transmembrane interactions between CD44 isoforms and cytoskeletal proteins (i.e. ankyrin) may play a pivotal role in regulating tumor cell behavior during human prostate cancer development.
CD44是一种糖基化黏附分子，它可能对10个可能的外显子进行可变剪接，从而产生变异体异构体。肿瘤细胞表达的多种CD44变异体异构体已与转移和增殖行为相关联。在本研究中，我们对三种前列腺癌细胞系：ALVA-31、PPC-1和LNCaP上的CD44异构体表达进行了表征。使用逆转录聚合酶链反应，我们发现ALVA-31和PPC-1细胞表达多种CD44异构体，包括CD44s（标准形式）、CD44E（上皮形式）和一种含外显子14的形式。此外，还检测到两种较小的形式：一种使用外显子5内的替代供体剪接位点，另一种是完全缺失外显子5的新形式。ALVA-31和PPC-1细胞表达的CD44异构体似乎优先位于细胞表面。相比之下，LNCaP细胞在RNA或蛋白质水平上不表达任何CD44形式。PPC-1和ALVA-31细胞在裸鼠中均表现出肿瘤发生和侵袭性，而LNCap细胞表现出恶性程度较低的表型，这表明CD44变异体（CD44v）表达与侵袭性前列腺肿瘤行为之间存在相关性。功能表征显示，CD44介导前列腺细胞与细胞外透明质酸（HA）的黏附。此外，CD44胞质结构域特异性结合膜细胞骨架蛋白锚蛋白。双重免疫荧光标记和共聚焦显微镜分析表明，HA结合诱导HA受体（即CD44）形成帽状结构。重要的是，细胞内锚蛋白优先聚集在HA受体帽状结构下方。这些结果表明，诸如锚蛋白之类的细胞骨架蛋白与HA诱导的CD44介导的信号事件密切相关。最后，HA介导的CD44异构体与细胞骨架蛋白（即锚蛋白）之间的跨膜相互作用可能在人类前列腺癌发生过程中调节肿瘤细胞行为方面起关键作用。
